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Optimal investment and consumption with forward preferences and uncertain parameters
Get PDFWe introduce and analyze a class of forward performance criteria in incomplete markets in the presence of model ambiguity. Incompleteness stems from general investment constraints, while model uncertainty is represented by a convex and compact set of plausible model parameter processes. Following the max-min criteria in traditional (backward) robust control, we formulate similar criteria for the robust forward performance processes and focus on the rich class of time-monotone processes. We provide a novel PDE characterization and a semi-explicit saddle-point construction of the robust forward performance criteria and their optimal policies. Furthermore, we present additional results within the class of homothetic constant relative risk aversion (CRRA) processes. Within this class, we investigate the relationship between forward performance processes on wealth and those on consumption, establishing an interesting dominance through time
Fiber-optic parametric amplifier-based all-optical format conversion enabling optical networks interconnection with different modulation formats
No full textA fiber-optic parametric amplifier (FOPA)-based all-optical format conversion (AOFC) scheme is proposed and numerically simulated to achieve optical networks interconnection with different modulation formats. In this scheme, the power transfer function (PTF) and the relative phase shift (RPS) functions between the input and output optical signals for the single-pump FOPA are derived and numerically analyzed. For the input 20 Gbps bipolar 4-ary pulse amplitude modulation (PAM4) signal, it can be converted into a BPSK signal (BPSK1) based on the power saturation characteristic of the PTF. By adjusting the input power of the input PAM4 signal, it can also be converted into a level-swapping PAM4 signal based on the single-pump FOPA. When the level-swapping PAM4 signal is sent into the single-pump FOPA with suitable power again, another BPSK signal (BPSK2) could also be generated. When the PAM4-to-BPSK format converter based on the single-pump FOPA is combined with the dual-pump FOPA (namely phase-sensitive amplifier, PSA), the 16-ary quadrature amplitude modulation (16QAM) signal can also be de-aggregated into four BPSK signals or two quadrature phase shift keying (QPSK) signals. The constellation diagrams, the power waveforms, the error vector magnitude (EVM) and the bit error rate (BER) of the relevant optical signals are measured to evaluate the scheme performance. The scheme can be deployed at the optical gateway to realize optical networks interconnection using different modulation formats
Generalization of scaled deep ResNets in the mean-field regime
No full textDespite the widespread empirical success of ResNet, the generalization properties of deep ResNet are rarely explored beyond the lazy training regime. In this work, we investigate scaled ResNet in the limit of infinitely deep and wide neural networks, of which the gradient flow is described by a partial differential equation in the large-neural network limit, i.e., the mean-field regime. To derive the generalization bounds under this setting, our analysis necessitates a shift from the conventional time-invariant Gram matrix employed in the lazy training regime to a time-variant, distribution-dependent version. To this end, we provide a global lower bound on the minimum eigenvalue of the Gram matrix under the mean-field regime. Besides, for the traceability of the dynamic of Kullback-Leibler (KL) divergence, we establish the linear convergence of the empirical error and estimate the upper bound of the KL divergence over parameters distribution. Finally, we build the uniform convergence for generalization bound via Rademacher complexity. Our results offer new insights into the generalization ability of deep ResNet beyond the lazy training regime and contribute to advancing the understanding of the fundamental properties of deep neural networks
Single step silicon carbide heteroepitaxy on a silicon wafer at reduced temperature
Get PDFA single step growth approach for wafer-scale homogeneous cubic silicon carbide (3C-SiC) heteroepitaxy, using chemical vapour deposition (CVD), on a silicon (Si) substrate is demonstrated. Residual biaxial tensile strain causing a wafer bow is eliminated in the 3C-SiC epilayer via in-situ defects engineering and heteroepitaxy at reduced temperature. Thermal mismatch between the 3C-SiC epilayer and substrate is minimised by a substantial reduction of growth temperature, down to ∼1000 °C. Heteroepitaxy of high quality, fully relaxed 3C-SiC epilayers with minimal wafer bow is demonstrated, made possible by careful process optimisation. Unusually very high growth rate of 3C-SiC of > 10 µm/hr is achieved. At the same time the epilayer is free from any other silicon carbide (SiC) polytype inclusions. Moreover, the reduced growth temperature unlocks the ability to deposit high quality 3C-SiC epilayers within traditional Si-based cold walled CVD reactors, enabling the growth of such thin films on unprecedently high volumes and wafer diameters up to 300 mm and above
Custodianship across generations : preserving the practice of vinyl record manufacturing
No full textDrawing on a global, longitudinal case study of the vinyl record manufacturing practice following a global decline in sales, we examine the work undertaken to preserve it over time. Our process model of practice preservation highlights that a declining practice may persist across generations if it is made more accessible and resilient by reducing its dependence on specific types of meanings, materials and competences that risk being lost. Our analysis suggests that these outcomes depend on the work of two types of custodians (legacy professionals and new enthusiasts) in terms of diversifying the practice to accommodate multiple configurations of meanings, materials and competences, thus constituting new practice variants, as well as supporting the continued enactment of variants over time by engaging in processes we label propping up, recovering, replenishing and releasing. In addition to developing a rich understanding of preservation, our findings contribute to a nuanced perspective on practice evolution by conceptualizing a practice as comprising multiple, potentially fluid variants. Moreover, by highlighting inclusive custodianship processes, which differ from gatekeeping and guarding so far emphasized, and by unpacking the role of materials to complement the traditional emphasis on symbolic elements, our findings enrich the nascent custodianship literature
Dataset to support : The hyporheic exchange of microplastics
No full textThe transport of microplastics in the hyporheic zone remains poorly understood with few studies attempting to quantify microplastic hyporheic exchange processes. A laboratory scale erosimeter was utilized in combination with fluorometric techniques to quantify the dispersion of 3D-pore scale stained microplastics across the hyporheic zone. Rhodamine WT dye, Polypropylene (PP), polyethylene (PE), and polymethyl methacrylate (PMMA) were well-mixed within the riverbed and individually tested using solute transport theory for three sediment diameters and five bed shear velocities (u_*) found in the natural environment. Effective dispersion coefficients for solutes significantly differed from that of PE and PMMA in most cases, where a limit as to how slow they could disperse was observed and a method for predicting polymer dispersion was proposed. When u_* ≥ 0.0304 m/s, PMMA followed the same pathways as solutes and solute transport models were successfully implemented to predict its fate. PP near the riverbed interface ascended to the surface but flocculation and aggregation deeper in the riverbed prevented dispersion calculations. When polymer buoyancy becomes the dominant process, high concentrations of lighter than water microplastics ascend into the water column and high concentrations of denser than water microplastics descend through pore water into groundwater systems. Unless density modification processes occur, pelagic organisms will be more exposed to polymers with densities 1 g/cm³ in fluvial systems. These findings highlight polymer density and aggregation ability as major factors for determining microplastic fate at lower velocities
Sovereignty and the persistence of the aesthetic
Get PDFBritish constitutional thought tends to understand sovereignty in legalistic terms, with the concept often equated with the doctrine of parliamentary sovereignty. As Loughlin and Tierney have recently argued, this approach obscures the political considerations which undergird the legal precept. In this article we argue that this approach misses a third, and essentially important, dimension to sovereignty. Law, politics and aesthetics all play equally important parts in constituting the essential structure of the concept. We elaborate this claim through a reading of some prominent accounts of sovereignty within the history of political modernity. At bottom, aesthetics is concerned with the ways in which the body's senses are stimulated and ordered; it therefore includes pictorial representation, ideation and imagination, as well as affect, instinct and habituated feeling. We argue that these different elements are usefully understood as all pertaining to a distinctive, and persistent, aesthetic dimension which is essential to the sovereignty concept
